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org/springframework/scheduling/backportconcurrent/ConcurrentTaskExecutor.java
/*
 * Copyright 2002-2009 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.scheduling.backportconcurrent;

import java.util.concurrent.Callable;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;

import edu.emory.mathcs.backport.java.util.concurrent.Executor;
import edu.emory.mathcs.backport.java.util.concurrent.Executors;
import edu.emory.mathcs.backport.java.util.concurrent.RejectedExecutionException;

import org.springframework.core.task.TaskRejectedException;
import org.springframework.scheduling.SchedulingTaskExecutor;

/**
 * Adapter that takes a JSR-166 backport
 <code>edu.emory.mathcs.backport.java.util.concurrent.Executor</code> and
 * exposes a Spring {@link org.springframework.core.task.TaskExecutor} for it.
 *
 <p><b>NOTE:</b> This class implements Spring's
 {@link org.springframework.core.task.TaskExecutor} interface (and hence implicitly
 * the standard Java 5 {@link java.util.concurrent.Executor} interface) as well as
 * the JSR-166 {@link edu.emory.mathcs.backport.java.util.concurrent.Executor}
 * interface, with the former being the primary interface, the other just
 * serving as secondary convenience. For this reason, the exception handling
 * follows the TaskExecutor contract rather than the backport Executor contract, in
 * particular regarding the {@link org.springframework.core.task.TaskRejectedException}.
 *
 <p>Note that there is a pre-built {@link ThreadPoolTaskExecutor} that allows for
 * defining a JSR-166 backport
 {@link edu.emory.mathcs.backport.java.util.concurrent.ThreadPoolExecutor} in bean
 * style, exposing it as a Spring {@link org.springframework.core.task.TaskExecutor}
 * directly. This is a convenient alternative to a raw ThreadPoolExecutor
 * definition with a separate definition of the present adapter class.
 *
 @author Juergen Hoeller
 @since 2.0.3
 @see edu.emory.mathcs.backport.java.util.concurrent.Executor
 @see edu.emory.mathcs.backport.java.util.concurrent.ThreadPoolExecutor
 @see edu.emory.mathcs.backport.java.util.concurrent.Executors
 @see ThreadPoolTaskExecutor
 */
public class ConcurrentTaskExecutor implements SchedulingTaskExecutor, Executor {

  private Executor concurrentExecutor;


  /**
   * Create a new ConcurrentTaskExecutor,
   * using a single thread executor as default.
   @see edu.emory.mathcs.backport.java.util.concurrent.Executors#newSingleThreadExecutor()
   */
  public ConcurrentTaskExecutor() {
    setConcurrentExecutor(null);
  }

  /**
   * Create a new ConcurrentTaskExecutor,
   * using the given JSR-166 backport concurrent executor.
   @param concurrentExecutor the JSR-166 backport concurrent executor to delegate to
   */
  public ConcurrentTaskExecutor(Executor concurrentExecutor) {
    setConcurrentExecutor(concurrentExecutor);
  }


  /**
   * Specify the JSR-166 backport concurrent executor to delegate to.
   */
  public final void setConcurrentExecutor(Executor concurrentExecutor) {
    this.concurrentExecutor =
        (concurrentExecutor != null ? concurrentExecutor : Executors.newSingleThreadExecutor());
  }

  /**
   * Return the JSR-166 backport concurrent executor that this adapter
   * delegates to.
   */
  public final Executor getConcurrentExecutor() {
    return this.concurrentExecutor;
  }


  /**
   * Delegates to the specified JSR-166 backport concurrent executor.
   @see edu.emory.mathcs.backport.java.util.concurrent.Executor#execute(Runnable)
   */
  public void execute(Runnable task) {
    try {
      this.concurrentExecutor.execute(task);
    }
    catch (RejectedExecutionException ex) {
      throw new TaskRejectedException(
          "Executor [" this.concurrentExecutor + "] did not accept task: " + task, ex);
    }
  }

  public void execute(Runnable task, long startTimeout) {
    execute(task);
  }

  public Future<?> submit(Runnable task) {
    FutureTask<Object> future = new FutureTask<Object>(task, null);
    execute(future);
    return future;
  }

  public <T> Future<T> submit(Callable<T> task) {
    FutureTask<T> future = new FutureTask<T>(task);
    execute(future);
    return future;
  }

  /**
   * This task executor prefers short-lived work units.
   */
  public boolean prefersShortLivedTasks() {
    return true;
  }

}